To energize multiple electrodes in a plasma source using a single RF power source, one needs to split the power into multiple channels. In the case of a plasma source topology with alternate electrodes 180 degrees out of phase with each other—such as that described in PCT/EP2006/062261 the content of which is incorporated herein by reference, where each of the electrodes may be out of phase with that of its neighbor, then it is useful to be able to provide push-pull pairs.
A classical solution to this problem would be to use a 180-degree splitter, followed by a series of N:1 splitters, where 2:1 and 4:1 splitters are typical in high power application, and higher values of n can be found for low power cases. Phase errors between output channels will typically be a couple of degrees, amplitude imbalance of 5%, and power loss of 3%; To create a 1:128 divider using a series of 2:1 splitters would end up in substantial power loss and errors in power to a specific electrode receiving only 70% of the power it should receive (0.95^7). In addition, the systems only function properly with the input and output impedances are matched, typically at 50 Ohms. Because the plasma load on the electrode will be substantially non-50-Ohm, an impedance matching network will be required between the final stage splitter output and the electrode for each electrode. This adds to the cost, complexity, and electrode-to-electrode variation for such a solution. Additionally, such a solution is only matched to specific electrode numbers, where the number of electrodes is factored into the types of splitters (for example a 7×10 electrode array would need the 180-degree splitter, a 5:1 splitter, and a 7:1 splitter) so each solution could require a different engineering solution for the splitters. Further still, the high power splitters (particularly odd-number splittings like 5, 7) are frequency specific, so operating at different frequencies would require different engineering solutions.
For reasons of simplicity, cost savings, and uniformity, it is desirable to have a solution in which the impedance matching is done prior to the splitter, the power splitter is ‘passive’, the splitter is broad-band (same concept for VHF and UFH frequency range—30-3000 MHz), and that the splitter be able to perform 1:N splitting for large and arbitrary N (advantageously employing a similar design for, N=30, 32, 36 for 3×10, 4×8, 6×6 electrode arrays). There is a further need for a power splitter that can be implemented with high total power efficiency, and drive an output impedance that can drive the plasma electrodes directly and could be configured to drive pairs of electrodes in differential (push-pull) mode.